434 



Mr. J. Aitken. On some Phenomena [Apr. 28, 



white light reflected by the larger particles, any coloured reflected light 

 that may be present is masked. 



Green Sun. 



On a few occasions the sun has been observed to be of a decidedly 

 greenish colour, while on other occasions it has appeared blue. The 

 experiments which have been described in this paper seem to offer an 

 explanation of this phenomenon. For a number of days in the begin- 

 ning of September, 1883, the sun was seen of a decidedly blue or 

 green colour in India, Trinidad, and other places. Most of the 

 observers who have written on the subject have linked this phenomenon 

 with the eruption of Krakatao, which took place just before the days 

 on which the green or blue sun was seen. From the light thrown on 

 the subject by these experiments, we see that an eruption, such as 

 that of Krakatao, would throw into the atmosphere a supply of the 

 very materials necessary for producing a green sun by means of small 

 drops of water, as it would send into the atmosphere an immense 

 quantity of aqueous vapour and an enormous amount of fine dust — a 

 combination the most favourable possible for producing a great 

 number of minute drops of water. 



Professor C. Michie Smith observed the green sun in India, and he 

 says: "The main features of the spectrum taken on the sun when 

 green were — 



"1. A very strong general absorption in the red end. 



"2. A great development of the rain-bands and of all other lines 

 that are ascribed to the presence of water-vapour in the atmo- 

 sphere."* 



It is evident, therefore, that one of the materials necessary for 

 producing this peculiar absorption by means of water-drops was 

 present in an unusual amount in the atmosphere at the time ; and it 

 also appears that a fine form of condensation had taken place, as Mr. 

 W. R. Mauley statesf that there was at the time a sort of haze all 

 over the sky, and from the letters of different observers .this haze 

 seems always to have accompanied the green sun. 



One almost wonders that a blue or green sun is not oftener seen, 

 as there are often present all the materials necessary for producing 

 these colours in the atmosphere. On a few occasions I have observed 

 the sun to be of a silvery whiteness, when the vapour in the upper air 

 was beginning to condense, and the sky was covered with a thin, filmy 

 cloud. It is, however, possible that this slightly bluish tint may 

 have been due to the sun being seen more in its natural colour than 

 usual, that is, made much less yellow by our atmosphere than it gene- 



* ' Nature,' toI. 30, p. 347. 

 f Ibid., vol. 28, p. 576. 



